Amino-functional siloxanes are used widely as constituents of textile-care compositions, in particular of textile-softening compositions, as constituents of detergents or cleaners for textiles and hydrophobicizing compositions. A large number of structural variations of this substance group is described in the prior art and is accessible via various production routes.
Polysiloxanes with high degrees of modification coupled with a chain length which can be variably adjusted irrespective of the nitrogen content are accessible by means of lateral functionalization of a polysiloxane with organic substituents containing amino groups. To achieve optimum application properties, it is advantageous to be able to adjust the nitrogen content of an amino-functional polysiloxane and the molar mass independently of one another.
The prior art discloses a large number of documents relating to laterally modified aminosiloxanes. The basically catalyzed equilibration for the production, as explained, for example, in EP 1 972 330 in paragraphs [0154] and [0155], can lead, depending on the starting materials used, either to terminally dihydroxy-functional, laterally amino-modified polysiloxanes, or to laterally amino-modified polysiloxanes, the end chains of which are end-capped with trimethylsilyl groups. Compared to their structural analogues provided with free SiOH groups, such end-capped polysiloxanes have not only better storage stability without dilution, but also prevent gel-like precipitations and growths when handling aqueous emulsions of such polysiloxanes. These gel deposits are particularly undesired for applications in the textile sector.
According to the prior art, as is described for example in U.S. Pat. No. 7,238,768 B2, the condensation polymerization leads to amino-modified polysiloxanes with hydroxyl groups or alkoxy groups at the chain ends. The catalysts used are carboxylic acids. The unpublished patent application DE 102010042861.2 describes a carboxylic-acid-catalyzed condensation polymerization which makes accessible hydrolysis-stable polysiloxanes with trimethylsiloxy groups at the chain ends and different lateral modifications in defined ratios.
U.S. Pat. No. 6,171,515 B1 describes end-capped and dialkoxy-functional aminopolysiloxanes which, in a synthesis step downstream of the siloxane polymerization, undergo a functionalization of the primary and secondary amino groups with epoxy-functional monomers, such as, for example, glycidol. A similar functionalization of aminosiloxanes with alkylene oxides is described in EP0399706. Further functionalizations of amino-functional polysiloxanes with glycerol carbonate or gluconolactone are described in EP 1 972 330 and in J. Phys. Chem. B 2010, 114, 6872-6877.
Amino-functional polysiloxanes are being continually improved in order to impart advantageous effects to the textile sheet materials treated therewith, such as, for example, a textile-softening effect, crease resistance and/or to reduce the harmful or negative effects which can arise during cleaning and/or conditioning and/or wearing, such as, for example, fading, greying, etc. Moreover, as well as a good soft feel of the fabric, a further aim is to achieve an adequate hydrophilicity. One disadvantage of textile-softening formulations based on polysiloxanes of the prior art consists in the oxidation sensitivity of the nitrogen-carrying groups. Both the amino-functional polysiloxanes and also the formulations thereof have an increasing yellow coloration depending on the storage conditions. Furthermore, the viscosity of the polysiloxane can increase to the point of gelation during storage. Unfavourable processing conditions during production, such as, for example, thermal stress, can adversely affect the storage stability of the amino-functional siloxane or formulations thereof or even lead to gelation during the synthesis.
The prior art, as illustrated by way of example in WO 1998019665 or DE 102009048978, describes the use of reducing agents such as, for example, sulphites, for stabilizing amine-containing formulations. In order to minimize the oxidation potential, the alkaline pH values of the amine-containing formulations are shifted to the neutral to weakly acidic range by adding mild soluble acids.
In view of the disadvantages of the prior art, there is a need for textile-softening polysiloxanes with increased storage stability. There is also a need for a production process which makes accessible comparatively low-viscosity, storage-stable amino-functional polysiloxanes.